1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to converting an input color space, and more particularly, to converting a color signal of an input color space into a color signal of a printer-output CMYK color space CMYKPrinter using a L*a*b*sRGB-to-CMYKPrinter lookup table.
2. Description of the Related Art
In order to meet various user demands, the functions of digital image devices such as monitors, scanners, or printers have been diversified and improved. Digital image devices may adopt different color spaces or color models according to their purpose of use.
Color models are classified into device-dependent color models and device-independent color models. Examples of the device-dependent color models include red-green-blue (RGB) models and cyan-magenta-yellow-black (CMYK) color models which are a type of subtraction color space models. Examples of the device-independent color models include Commission Internationale de l'Eclairage (French: International Commission on Illumination—standardization body) (CIE) color models such as a CIEL*a*b* model, a CIE XYZ model, and a CIE LUV model. These CIE color models are theoretical color models developed by the International Commission on Illumination (ICI), which is an organization for developing a set of universal illumination standards. The CIE XYZ model defines a set of three tristimulus values, i.e., R, G, and B values, as a combination of three axes, i.e., the X-axis, the Y-axis, and the Z-axis. CMYK color spaces are widely used in the field of printing, whereas RGB color space are widely used in the field of computer graphics based on computer monitors, e.g., the field of web graphics.
Digital image devices which receive and output digital images may adopt different trichromatric systems to divide and/or synthesize colors, and thus represent the same colors differently. In addition, the type and intensity of trichromatic light may vary from one image display device to another. Thus, image display devices may display the same image signal in different colors from one another. Moreover, printers using different trichromatic inks or different colors of paper from one another may output the same color differently. Since the color mixing principles generally adopted by image display devices are opposite to the color mixing principles generally adopted by printers, a color gamut of image display devices is inevitably different from a color gamut of printers, and thus, image display devices and printers are likely to represent the same image signal in different colors.
In order to address this problem, a variety of techniques for converting a color signal of a color space to be compatible with the color representation properties of digital image devices have been developed. Examples of related color space conversion methods include a method for converting a color signal of an L*a*b* color space into a color signal of a CMYK color space, and a method for converting a color signal of a CMYK color space into a color signal of a C′M′Y′K′ color space.
However, in the related L*a*b* color space-to-CMYK color space conversion method, an input color space is converted first into a standard RGB (sRGB) color space regardless of the type of the input color space. Therefore, the related L*a*b* color space-to-CMYK color space conversion method may not be able to produce optimum color space conversion results for various types of input color spaces such as a Specifications for Web Offset Publications (SWOP) CYMK color space, an Adobe RGB color space, and an scRGB color space. The related CMYK color space-to-C′M′Y′K′ color space conversion method cannot be applied to input color signals which belong to an RGB color space (such as an sRGB color space, an Adobe RGB color space, or an scRGB color space) but can only be applied to input color signals which belong to an CMYK color space.